Many materials ranging from food-stuffs to sewage sludge and including both liquids and particulate materials must have water removed, for example to produce marketable products or to facilitate transportation and/or disposal of the material. Processes for dehydration involve moving the material through a zone of heated air which is usually blown at high velocity. The dried material is then separated from the air and collected. Heat for evaporation of water during these processes is usually provided by gas or oil, depending on the nature of the materials and the requirements of the end product.
It has been known for many years that the rate of drying can be greatly increased by imposing sound waves on the material in the presence of heated air. For example, this phenomenon is discussed in "Sonic Drying" by Robert S. Soloff (the Journal of the Acoustical Society of America - Volume 36 Number 5, May 1964). However, the additional cost of the energy required for the sound generator has generally not been thought justified commercially.
Pulsating combustion has been recognized as an obvious method of providing the heat, high velocity and intense sonic waves required for dehydration. This principle was first used to propel the flying bomb of World War II and was later used in highly efficient heating apparatus such as the Hydropulse Boiler and the Lennox Pulse Furnace.